1. Field of the Invention
The present invention relates generally to apparatuses and methods for transferring, focusing and purging powder for direct printing at low temperature and, more particularly, to an apparatus and method for transferring, focusing and purging powder for direct printing at low temperature which are configured to rapidly and smoothly conduct a series of processes for directly printing metal or ceramic powder on a substrate in a variety of patterns at a micro scale at low temperature without conducting additional heat treatment: aerosolizing powder through a momentary pulse type valve control, discharging a desired amount of powder through a nozzle, directly applying the powder to the surface of a work target such as a substrate in a focused form to print a desired pattern, stabilizing powder after discharge of the desired amount of powder has completed, and then returning the powder.
2. Description of the Related Art
Inkjet printing and direct printing technology using liquefied ink in a manner similar to that of the inkjet printing are used to precisely print a predetermined material on a substrate in a desired pattern.
Recently, studies on methods of manufacturing a variety of machines, electric elements or apparatuses in such a way that a desired pattern is directly printed at a desired position on a substrate using such a direct printing technology are actively being undertaken.
In such a printing technology, liquefied ink is used, and a piezo-actuator or the like is typically used to apply an ink droplet onto a substrate through a nozzle using the viscosity of ink.
However, the printing technology using ink is disadvantageous in that additional heat treatment is required because liquefied ink is used, it is difficult to produce a print result structure having a high aspect ratio, and it must depend on a wet process.
In an effort to overcome the above-mentioned problems, a method has been proposed, in which powder having micro- or nanometer-sized particles is discharged along with high-pressure transfer gas from a nozzle and is deposited on the surface of a substrate.
In detail, techniques such as an aerosol deposition method, a cold spray deposition method, a nano-particle deposition system, etc. are known. In these techniques, dry solid powder is accelerated by high-pressure transfer gas and is discharged from a nozzle, thus forming a functional pattern or a thin film on a substrate.
Generally, particles accelerated by high-pressure transfer gas to a high speed of several hundreds m/s or more collide with a substrate at high speed because of the force of inertia. On high speed collision a high-temperature area is partially formed on the surface of each particle.
As high-temperature areas are partially formed on the surfaces of the particles, when fine particles are deposited, very strong bonding force is applied between the particles, and they are very densely deposited.
Metal powder or ceramic powder is typically used as the fine particles. Particles such as polymer particles are also reported as producing promising deposition results.
Furthermore, with regard to the substrate, it is being reported that different kinds of powder can be deposited on a variety of substrates.
These techniques are advantageous in that a dry process can be used, and solid particles can be deposited on a substrate at low temperature or room temperature. However, cases where these techniques are used to directly print a precise pattern on a substrate are still rare.
The reason for this is because it is difficult to use transfer gas to form uniformly-dispersed particles from powder, that is, aerosolized powder in transfer gas, aeromechanically control a flow rate of aerosolized powder and a transfer timing of aerosolized powder, and accelerate particles at high speed and precisely deposit them on a portion of a substrate.
Furthermore, with regard to the conventional cold spray deposition process or the like, technical development and studies on deposition of various kinds of powder on a large area of a substrate have been mainly conducted, rather than on the application technique.
The following problems should be solved to deposit particles and precisely and directly print a very small sized pattern on a substrate using the conventional technique such as the above-mentioned cold spray deposition or the like.
Fine particle type powder must be enabled to be immediately aerosolized at a desired moment, the amount of particles transferred to a nozzle and a substrate and a transfer timing must be precisely controlled, and the transfer of aerosolized powder must be stabilized and the supply thereof must be interrupted immediately after a desired degree of printing process has been completed so that a small sized pattern can be printed.
Further, to precisely and directly print on a very small sized pattern on a substrate using particles, the particles must be enabled to be applied from the nozzle onto the substrate in a focused form. After a desired amount of particles has been discharged from the nozzle, the remaining powder must be rapidly stabilized such that the discharge operation is reliably finished.
In the conventional cold spray deposition method or the conventional method in which solid powder or particles are carried on transfer gas and deposited on a substrate, the transfer gas is typically provided from high-pressure compressed gas at a constant flow rate.
In a process of these conventional methods, because the speed of transfer gas and the speed of particles accelerated by the transfer gas must be increased and collision speed by the force of inertia must be increased so as to the quality of deposition, transfer gas having a high pressure of several tens MPa or more is used, or a vacuum chamber is used in such a way that a low pressure side is decompressed to be at a negative pressure so that a pressure difference between a high pressure side from which transfer gas is supplied and the low pressure side in which the substrate is disposed can be increased.
In the case of the cold spray deposition, high-pressure transfer gas of several tens Mpa or more is used, and a portion in which the substrate is disposed is maintained at atmospheric pressure.
In the aerosol deposition method or nano-particle deposition system, the deposition operation is conducted in a vacuum chamber, and transfer gas of several bar is typically used.
However, these conventional methods are problematic in that since transfer gas is continuously supplied only at a constant flow rate, it is difficult to increase a pressure difference, to a certain level, between a transfer gas supply side of high pressure and the substrate maintained at low pressure.
To solve the above-mentioned problem, a method, in which an area including a space in which a base material is disposed is intermittently sealed so that decompression can be intermittently amplified whereby a collision speed of aerosolized powder can be increased, was proposed in Korean Patent Application No. 10-2007-0002024.
Similarly, in Korean Patent Laid-open Publication No. 10-2008-0009160, a high pressure side and a low pressure side (atmospheric pressure) are separated from each other by a separation film (on-off valve). When the separation film is momentarily removed (the valve is momentarily opened), compression waves or shock waves are transmitted from the high pressure side to the low pressure side, whereby transfer gas and particles to be deposited on a substrate can be more effectively accelerated.
From these modified conventional patent applications, it can be appreciated that particles can be more effectively accelerated and a more satisfactory deposition result can be obtained in such a way that the high pressure side from which transfer gas is supplied and the lower pressure side in which powder and the substrate are disposed are separated from each other by an appropriate method, and a means for separating the high-pressure side and the low-pressure side from each other is momentarily and temporarily removed so as to accelerate transfer gas and particles.
However, although these modified conventional techniques can be easily used for large area deposition and coating, research and development on reducing the size of a deposition pattern and controlling the shape of the pattern and the position of deposition have not been sufficient.
In the conventional methods in which particles are accelerated by transfer gas and deposited on a substrate and in the modified conventional methods, critical problems in printing a precise pattern (mircroscale) on a substrate are that the amount of aerosolized powder supplied or sprayed onto the substrate for deposition is large, and research and development of a technique of controlling it has not been sufficient.
Direct printing techniques such as inkjet printing can manufacture a precise pattern, because ink droplets can be supplied by stages with the minimum amount necessary to manufacture the pattern.
However, with regard to the modified methods in which particles are deposited on a substrate in such a way as to accelerate them using transfer gas, research and development on a technique of supplying, by steps, the minimum amount aerosolized powder necessary to manufacture a precise pattern and controlling the size of the deposition pattern have been unsatisfactory.